The subject matter of the invention relates to a method for classifying the structured inner and/or outer surface of heat exchanger tubes which are seamless or have a longitudinal welded seam.
According to the state of the art, surface-structured tubes are preferably utilized for heat transfer processes. These tubes are usually manufactured without a seam or are provided with a longitudinal welded seam. As a rule the tubes are copper tubes.
Tubes with a structured surface have a larger surface area than plain tubes. Tubes with a large surface area are preferably utilized in heat exchanger systems. The goal is to achieve enhanced performance densities for smaller sized products and lighter weight construction. For this it is necessary to improve the performance of the individual tubes.
The classification of structured tubes is accomplished usually at a high expense and with much time through the determination and analysis of the geometric magnitudes identifying the structure, such as structure heights and element angles. Examples of geometric structure magnitudes are, among others, described in detail in the EP 0 148 609. Therefore, for the classification of a geometric surface structure many individual measurements are needed. Besides the considerable technical measuring requirements, an accumulation of measurement errors may still occur.
To determine the heat transfer characteristics of a heat exchanger tube, it is necessary to carry out extensive measurements on individual tubes or bundles of tubes on a special heat-transfer test facility. Based on the background of the enormously large multitude of geometrical structured elements there arises the demand for a clear technically measured classification of the structure finenesses and their heat performance characteristics utilizing equipment clearly less complex compared with the state of the art.
The basic purpose of the invention is therefore to provide in place of the expensive, heat transfer measurement of individual tubes a method for the quick, clear and reproducible classification of structured surfaces. In particular a technical measurement capability operating without contact has been discovered and with which it is not necessary for a tube sample ready for use to be present.
This has been accomplished by providing a method for classifying the structured inner and/or outer surface of heat exchanger tubes with a longitudinal welded seam, wherein in each case a defined sample of the structured band, which is provided for the manufacture of the heat exchanger tube, is placed onto a movable surface and moved therewith and subjected to a Doppler radar spectroscopy measurement using electromagnetic waves (microwaves) in the frequency range of 1 to 100 GHz, whereby the following magnitudes are compared to the standardized Doppler radar spectrum (standardized to the plain tube):
Surface integral A, average value m and variance S (or standard deviation xcfx81={square root over (S)}) as well as a method for classifying the structured inner and/or outer surface of seamless heat exchanger tubes, wherein in each case a defined sample is moved from the surface of the heat exchanger tube, which surface is unrolled in a plane, placed onto a movable surface moved with the surface and subjected to a Doppler radar spectroscopy measurement using electromagnetic waves (microwaves) in the frequency range of 1 to 100 GHz, whereby the following magnitudes are compared to the standardized Doppler radar spectrum (standardized to the plain tube):
Surface integral A, average value m and variance S (or standard deviation "sgr"={square root over (S)}).